The primary objectives of this project are to better understand the factors that lead to the development of secondary caries and to identify strategies to increase the service life of resin composite restorations. Restoration replacements due to secondary caries occupies a large portion of the dentist's practices. In 1999, 86 million composites were placed by dentists in this country and 122.7 million in 2006. The average replacement time is now only 5.7 years. Significant improvements in the long-term integrity of so many restorations could save the American people (by reducing costs of replacing restorations) many times the amount of money required to support this work. There is tremendous significance in the successful pursuit of this endeavor to benefit so many millions of people. We propose to study the effects of biofilm activity and dental resin composite compositions on the development of secondary caries. We will use a bioreactor model that utilizes conditions found in the oral environment to understand the role of microbial biofilms, salivary pellicles, and cyclic loading in the processes of secondary caries formation. While the bioreactor model establishes the conditions for the cyclic remineralization/demineralization attacks, we will use a variety of oral-simulating challenges and analytical methods to assess their effects on composite-restored teeth. We hypothesize that major contributors to defects at restoration margins include: interfacial stresses from contractions induced by polymerization shrinkage of resins, salivary esterases, acidogenic microbe-generated biofilms, and deformations from cyclic loading and oral thermal fluctuations. These can lead to subsequent staining, secondary caries, fractures, or other problems. The long-term goals of this project are to identify and prepare an optimally cross-linking composite composition resin that can restore defective teeth and defy environmental degradation (Aim 1); determine the effects of polymerization shrinkage on the development of degradation at the tooth-composite interface (Aim 2); understand the roles of salivary pellicles and microbial biofilms in the etiology of secondary caries' association with composite restorations (Aim 3); and develop beneficial biofilms in synergy with fluoride therapies that have the potential of retarding the onset of secondary caries (Aim 4). Our goal is to understand the physical, chemical and biological factors that determine the length of time a restoration lasts. With this understanding, we will develop more stable resin-based composites and methods to prevent the decay that limits the success of composite restorations. PUBLIC HEALTH RELEVANCE: This project is focused on developing strategies to increase the service life of resin composite restorations. Our goal is to understand the physical, chemical and biological factors that determine the length of time a restoration lasts. With this understanding, we will develop more stable resin-based composites and methods to prevent the decay that limits the success of composite restorations.